Process of pickling metals



Patented June 27, 1933 UNITED STATES PATENT OFFICE GEORGE L. MAGOUN, OF NITRO, WEST VIRGINIA, ASSIGNOR TO THE RUBBER SERVICE LABORATORIES COHJPANY, OF AKRON, OHIO, A CORPORATION OF OHIO PROCESS OF PICKLING METALS No Drawing. Application filed February The present invention relates to the cleaning and preservation of metallic surfaces, wherein the metal is in contact with a liquid of an acid nature. More particularly, the invention relates to the prevention of excessive pitting and embrittlement of a metal when subjected to a pickling process by treatment with a dilute solution of a mineral acid.

Certain objects of the present invention are to prevent the acid pickle liquor from attacking clean portions of the surface of a metal; to obviate over-pickling, embrittlement and pitting of the articles treated; to minimize the amount of metal lost in pickling; to increase the efficiency of the pickling operation; to prolong the effective life of the pickling bath; and particularly to facilitate the pickling operation. Other and further objects of the invention will be apparent from the following description and accompanying examples.

In the art of pickling, the metal is treated with a dilute acid to remove oxides such as rust, scale, and other deposits, after which the metal is preferably washed with water and dipped into an alkaline bath to remove c .f/thelast-traces of freeacid. The'acid re- W -moves-the rust and scale, but unfortunately,

from the pickling standpoint, unless some agent to prevent such action is present, it attacks the cleaned metal itself, thereby causing loss of metal and producing an evolution of hydrogen gas, which escapes into the air, carrying with it a fine spray of the acid liquor from the pickling bath and producing an atmosphere possessing corrosive properties and one which is injurious to health and damaging to equipment.

By the present invention, these objectionable features of the pickling process are substantially overcome or reduced to a minimum. To accomplish to as great an extent as possible the objects set forth in accordance with the present invention, there is added to the pickling bath a regulating agent or ingredient which acts to restrain the action of the acid from attacking clean metal but assists in removing the rust, scale and other deposits, or in other words, the regulator or inhibitor causes the acid selectively to re- IG, 1931. Serial No. 516,208.

move such materials without appreciably attacking the clean portions of the metal under treatment.

The pickle regulator or inhibitor, as disclosed in the present application, comprises j! ...!lle, iydederiyative of a reaction product of1an organic base. and a mercaptoarylthia- 20 e.

"'" In the examples hereinafter set forth for carrylng out the metal pickling process, conditions were imposed which duplicated, so far as possible, those commonly followed in commercial practice, so far as concerned acid concentrations and temperatures employed.

Test pieces of 30 gauge cold rolled tin plate steel stock, approximately 4 x 3 in dimension, were immersed in approximately 750 cc of a water solution of sulfuric acid contaming approximately 6% by weight of 66 B. acid to which had been added a small quantity of one of the preferred type of inhibitors. The loss in weight of the steel test pieces resulting from maintaining the strips in the pickle bath in the manner described for a definite period of time was then determined. The temperature of the pickling bath was maintained at from 8085 C. For the acid concentration set forth, commercial practice is to pickle at approximately 66 to 88 C. The results so obtained were compared with similar tests wherein the steel pieces were subjected, under the conditions set forth, to the action of an acid solution of the strength and for the time specified above, but containing no inhibitor.

Examples of the preferred class of materials may in general be prepared by heating the base with the mercaptoarylthiazole at a temperature suflicient to cause reaction (preferably below 160 C.) and then adding the aldehyde in the form of a liquid or gas to the product while maintaining the latter at a sui(t3al))le temperature (preferably below 160 One method whereby one of the preferred class of compounds, for examplean aldolderi ative of a reaction product of diphenyl- "guanidine and2 mercaptobenzothiazole, was

prepared follows:

nxammqr diphenylguanidine and substantially one molecular proportion of 2-mercaptobenzothiazole were placed in a suitable vessel and heated at approximately 155 C. for approximately fifteen minutes. After cooling, substantially one molecular proportion of aldol was added and the mixture heated sufficiently to melt the reactants together. The product thus formed was a resin that could readily be ground to a fine powder.

A portion of the product prepared as described aboi'e was incorporated in a pickling bath in the manner hereinbefore described. Thus, a steel test piece, 3" x 4 in dimension, cut from 30 gauge cold rolled tin plate stock, exposing approximately 24 square inches of surface and weighing 18.851 grams, was found to lose but 0.014 grams after 40 minutes pickling in 750 cc. of a (3% sulfuric acid solution containing 0.047 grams of the in hibiting product hereinbet'ore described. A similar test piece weighing 18.499 grams and treated in the same manner, but without the use of any inhibitor lost 0.519 grams. Thus it is shown that when the aldol derivative of the reaction product of diphenylguanidine and 2-1nercaptobenzothiazole is employed as an inhibitor, the loss in weight per square inch of surface exposed corresponds to 0.00058 grams, whereas when no inhibitor is employed in the test described. the loss per square inch of surface exposed corresponds to 0.02163 grams. The loss in weight per square inch of surface exposed is only 2.7 per cent as great by employing the inhibitor set forth as results if no inhibitor is employed in the pickling process. A greater saving in metal losses results from the use of a larger amount of the inhibitor than that employed in the example. Moreover, the steel plates pickled in the presence of the inhibitor set forth are clean and not stained upon removal from the pickle bath.

Other aldehyde derivatives of a reaction product of an organic base and a mercaptoa-rylthiazole have been prepared in a manner analogous to that hereinbefore set forth and tested as inhibitors in a pickling bath in the manner hereinbefore described. Thus, the following products were so prepared and tested:

Compound A.React-ion product of substantially 175 parts by weight of hexamethylene tetramine and substantially 313 parts by weight of 2-mercaptobenzothiazole, further reacted with a substantially equal weight of butyraldehyde.

Compound B.Reaction product of substantially one molecular proportion of isoamylamine and substantially one molecular proportion of Q-mercaptobenzothiazole, further reacted with substantialy one molecular pro ortion of aldol.

o'mpound C.-Acetaldehyde derivative of the reaction product of substantially one molecular proportion of piperidine and substantially one molecular proportion of 2- mercaptobenzothiazole.

Compound D.The product formed by reacting substantially 410 parts by weight of the reaction product of substantially equimolecular proportions of acetaldehyde-ainmonia and Q-mercaptobenzothiazole with substantially 30 parts by weight of crotonaldehyde.

Compound E .-The product formed by reacting together substantially equimolecular proportions of alpha-phenylbiguanide and 2- mercaptobenzothiazole, and then saturating the product so formed with acetaldehyde.

Compound F .Reaction product of substantially one molecular proportion of 2, 4- diamido-diphenylamine and substantially two molecular proportions of 2-mercaptobenzothiazole, further reacted with substantially one molecular proportion of acefaldehyde.

Compound G.Reaction product of substantially one molecular proportion of parapara-diamido-diphenylmethane and substantially one molecular proportion of Q-mercaptobenzothiazole, further reacted with substantially one and one-half molecular proportions of furfural.

Compound H .Reaction product of substantially one molecular proportion of parapara-diainido-diphenylmetliane and substantially one molecular proportion of Q-mercaptobenzothiazole, further reacted with substantially one and one-half molecular proportions of alpha-ethyl-beta-propyl-acrolein.

Compound l.-Reaction product of substantially one molecular proportion of parapara-diamido-diphenylmethane and substantially one molecular proportion of 2-mercaptobenzothiazole, further reacted with substantially one and one-half molecular proportions of formaldehyde.

Compound J .-The product formed by reacting substantially equimolecular proportions of para-para-diamido-diphenylmethane and Q-mercaptobenzothiazole, and then saturating the product so formed with acetaldehyde.

Compound K.Reaction product of substantially 28 parts by weight of hexamethylene-tetramine and substantially 50 parts by weight of EZ-mercaptobenzothiazole, further reacted with substantially 6.5 parts by weight of crotonaldehyde.

Compound L.The product formed by reacting substantially equimolecular proportions of alpha-ortho-tolyl-biguanide and 2- mercaptobenzothiazole and then saturating the product so formed with crotonaldehyde.

The results of the tests obtained on immersing steel test strips of 30 gauge cold rolled tin plate stock 3 x 4 in dimension, for 40 minutes in 750 cc. of 6% by weight of 66 B. sulfuric acid at C., in the presence ZDZ. UUIVIIUSI l IUNS,

'mercaptonaphthiazole and the like. and the of the indicated quantity of one of the above described inhibitors, are given in Table I.

Table I Yii'eigbt Y Weight of Weight 0! 055 m Inhibiting compound g fi steel strip steel strip g gig employed emplo ed before after g or y pickling pickling Surface exposed Grams Grams Grams Grams Compound A 0. 047 18. 467 18. 449 0. 00075 Compound B s- 0. 047 18. 793 18. 781 0. 00050 Compound C 0. 047 18. 922 18. 905 0. 00071 Compound D. 0.028 18. 654 18.631 0.00096 Compound E. 0. 047 18. 305 18. 285 0. 00083 Compound F. 0 047 18. 660 18. 644 0. 00007 Compound G. 0. 047 18.837 18.811 0.00108 Compound H 0. 017 18. 449 18.433 0. 00067 Compound I. 0. 047 18. 623 18. 603 0. (D083 Compound .1 0. 017 17. 559 17. 539 0. 00083 Compound K. 0. 047 17. 609 17.588 0. 00088 Compound L 0. 047 18. 172 18. 145 0. 00113 None None 18.490 17. 980 0. 02163 It is apparent from the data set forth that the preferred class of materials constitutes an important and highly efiicacious group of inhibitors, as in all cases wherein one of the preferred inhibiting compounds was incorporated in the pickle liquor, there resulted a great saving in the loss in weight of the steel test strips as compared with that resulting when no inhibitor was employed.

As a further example of the preferred class of inhibitors, there was prepared a reaction product of substantially one molecular proportion each of para-para-diamidodiphenylmethane and e merc'aptbbenz'ot-hiazole. and "this product was further reacted with substantially one molecular proportion of crotonaldehyde. The compound thus prepared was tested in the manner hereinbefore described and found to possess the inhibiting qualities of the preferred class of compounds.

i jm e enamples of'this preferred class of iuhibitors niaybe prepared by reacting other organic bases with mercaptoarylthiazoles and further reacting the products thus formed with various aldehydes. Thus. for example, diethylamine. pyrrolidine, tri- .c tl 1 anolamine, tributylamine,'diplienylaniinc. and the like. maybe reacted with mercaptobenzothiazole, mercaptotolylthiazole,

products thus formed may be further reacted w th aeetaldehyde. crotonaldehyde. aldol, furfural. and the like. and the products thus obtained employed an inhibitors in the manner hereinbefore set forth.

Other modes of employing inhibitors of the class hereinbefore set forth in the acid pickling of metals are apparent to those skilled in the art to which this invention pertains. The products described additionally may be employed in the presence of foaming agents, ionizable substances or other m terials ordinarily used. Again other acids than sulfuric acid may be employed Examiner in the pickle bath. Thus hydrochloric acid as well as other inorganic acids may be em ployed in the pickle bath in conjunction with the preferred class of inhibitors in the manner hereinbefore set forth.

lVhat is claimed is:

1. A process of pickling iron and steel products which comprises subjecting; the metal to be pickled to the action of a substantially non-oxidizing mineral acid solution to which has been added a small proportion of an aliphatic aldehyde derivative of a reaction product of an organic amine and a mercaptoarylthiazole.

2. A process of pickling iron and steel products which comprises subjecting the metil to be pickled to the action of a substantially non-oxidizing mineral acid solution to which has been added a small prop *rtion of an aliphatic aldehyde derivative of a reaction product of an organic amine attd a m:rcaptohenzothiazole.

3. A process of pickling iron and steel proc ucts which comprises subjecting the m tal to he pickled to the action of a sulfuric acid solution to which has been added a small proportion of an aldehyde derivative of a reaction product of an organic amine and a 1nercaptobenzothiazole.

4. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution to which has been added a small proportion of an aldehyde derivative of a reaction product of an aliphatic amine and a mercaptobenzothiazole.

5. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of an aldehyde derivative of a reaction product of an organic polyamine and a mercaptobenzothiazole.

6. A process of pickling iron and steel products which comprises Sub ecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of an aliphatic aldehyde derivative of a reaction product of an organic polyamine and a mercaptobenzothiazole.

7. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of an aliphatic aldehyde derivative of a reaction product of a guanidine and a mercaptobenzothiazole.

8. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of an aldol derivative of a reaction product of diphenylguanidine and Q-mercaptobenzothiazole.

9. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of the product formed by reacting substantially one molecular proportion of diphenylguanidine with substantially one molecular proportion of 2-mercaptobenzothiazole and .further reacting the product thus formed with substantially one molecular proportion of aldol.

10. A pickling bath for iron and steel products which comprises a substantially nonoxidizing mineral acid solution to which has been added a small proportion of an aliphatic aldehyde derivative of a reaction product of an1 organic amine and a mercaptoarylthia- 20 e.

11. A pickling bath for iron and steel products which comprises a substantially nonoxidizing mineral acid solution to which has been added a small proportion of an aliphatic aldehyde derivative of a reaction product of an organic amine and a mercaptobenzothiazole.

12. A pickling bath for iron and steel products comprising a sulfuric acid solution to which has been added a small proportion of an aldehyde derivative of a reaction product of an organic amine and a mercaptobenzothiazole.

13. A pickling bath for iron and steel products comprising a sulfuric acid solution to which has been added a small proportion of an aldehyde derivative of a reaction product of an aliphatic amine and a mercaptobenzothiazole.

14. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of an aldehyde derivative of a reaction product of an organic polyamine and a mercaptobenzothiazole.

15. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of an aliphatic aldehyde derivative of a reaction product of an organic polyamine and a mercaptobenzothiazole.

16. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of an aliphatic aldehyde derivative of a reaction product of a guanidine and a mercaptobenzothiazole.

17 A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of an aldol derivative of a reaction product of diphenylguanidine and Q-mercaptobenzothiazole.

18. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of the product formed by reactin substantially one molecular proportion of diphenylguanidine with substantially one molecular proportion of 2- mercaptobenzothiazole and further reacting the product thus formed with substantially one molecular proportion of aldol.

19. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a mineral acid solution to which has been added a small proportion of an aldehyde derivative of a reaction product of an organic amine and a mercaptoar lthiazole.

20. A pic ing bath for iron and steel prod ucts which comprises a mineral acid solution to which has been added a small proportion of an aldehyde .derivative of a reaction product of an organic amine and a mercaptoarylthiazolc.

In testimony whereof I hereunto aflix my signature.

GEORGE L. MAGOUN. 

